1. Field of the Invention
The present invention relates to pumps that are used in the secondary recovery of oil, namely recovery of oil that will not flow to the surface via downhole pressure. Even more particularly, the present invention relates to an improved downhole oil well pump that includes a flexible pumping member activated with hydrostatic pressure of liquified gas (such as, for example, butane) and a closed circuit flow path for the gas that includes a compressing step to recompress the butane to liquid form after it has been expanded to gaseous state following the pumping cycle of the pump.
2. General Background
In the pumping of oil from a downhole oil well environment, it has been known to use mechanical pumps such as rod pumps to lift oil to the earth's surface when that oil will not flow because of low formation pressure. Such pumps have been in use for years and are commercially available from a number of manufacturers such as Camco, Otis, Halliburton and others. These same manufacturers supply gas lift valves that can be used to "lift" oil from a sluggish well. Gas lift valves are valving structures that are positioned at vertically spaced intervals along the production tubing. They are activated at varying pressures, providing pressurized gaseous injection at various levels in the well to help urge the oil upwardly.